Patent Document 1 describes an additive agent (a monothioester compound) for a rubber composition represented by the general formula R3R2N—X—Y—R1. In the formula, Y can be a thioester bond, and specifically, octanethioic-S-acid dimethylaminoethyl, octanethioic-S-acid 2-diethylaminoethyl, propanethioic-S-acid 2-piperazinoethyl and the like are used. In the Patent Document, Mooney viscosity which shows processability, Mooney scorching time which shows processing stability, tan δ which shows low exothermicity, and rolling resistance were measured, and a good Mooney scorching time was not obtained.